Purple nutsedge (Cyperus rotundus) and sicklepod (Senna obtusifolia) response to glyphosate mixtures with ALS-inhibiting herbicides

Greenhouse studies were conducted to evaluate potential interactions among glyphosate mixtures with five acetolactate synthase (ALS)-inhibiting herbic ides (chlorimuron, imazamox, imazaquin, MON 12,000, or pyrithiobac) for the control of purple nutsedge and sicklepod at two growth stages. Herbicides were tested alone at 0.5 x and 1 x rates (Ix being suggested use rate for t hese herbicides) and in combination with glyphosate at 560 (0.5x) and 1,120 (1x) g ai/ha on 3-wk-old plants and at 1,120 g/ha on B-wk-old plants. Glyp hosate alone at 1,120 g/ha gave complete control of purple nutsedge and at least 78% control of sicklepod regardless of growth stage. In 3-wk-old purp le nutsedge plants, three of the 20 herbicide combinations were antagonisti c and 17 combinations were additive, whereas all five combinations were add itive in B-wk-old plants. In sicklepod, eight combinations were antagonisti c and 12 combinations were additive in 3-wk-old plants, and all five combin ations were antagonistic in 6-wk-old plants. In 3-wk-old plants, the glypho sate (0.5x) plus imazaquin (0.5x) combination resulted in highest antagonis m in purple nutsedge control (79%), and the combination of glyphosate (0.5x ) plus imazamox (0.5x) resulted in highest antagonism in sicklepod control (54%). These results indicate that mixing chlorimuron, imazamox, imazaquin, MON 12,000, or pyrithiobac with glyphosate does not increase glyphosate ef ficacy on purple nutsedge or sicklepod.